This invention relates to an improved sheet metal clip. More particularly, it relates to an improved stack of sheet metal clips in which the clips are collated or interconnected for storage or for use in a clinching tool.
It is well known in the mattress and bedding industries to join wire and spring elements together with a sheet metal clip. A typical clip for use in such applications is generally U-shaped having an arcuate crown portion and oppositely spaced leg portions depending from the crown portion. Such a U-shaped clip is clamped onto wires or bedsprings by a clinching tool. A typical clinching tool for use with U-shaped clips includes a generally J-shaped jaw into which the leading clip in a stack of clips is indexed. The clinching tool has a blade which upon actuation thrusts downwardly to shear off the leading clip from the stack of clips and thereby clamp the leading clip around a pair of wires positioned within the J-shaped jaw. A typical clinching tool of the type described is illustrated in U.S. Pat. No. 2,574,811.
The sheet metal clips are collated and aligned in a stack configuration such that each clip is similarly oriented and in abutting relationship with the adjacent clip. The clips are maintained in the stacked configuration for both storage and for use with the clinching tool. For storage, the stack of clips is typically wound under tension upon a cylindrical core member to provide a compact spool of interconnected clips. For use, the stack of clips is unwound under tension beginning with the free end of the stack, which is inserted into the clinching tool for use in clamping a plurality of wires together.
The clips must be interconnected in the stacked configuration so that they are sufficiently flexible to be wound onto a spool and also be interconnected with sufficient strength to withstand the high tensile forces associated with the winding and unwinding of the stack of clips upon the spool. However, the method of joining the clips in a stack configuration, while possessing the requisite strength and flexibility, cannot interfere with the operation of existing clinching tools. Likewise, the structure used to interconnect the sheet metal clips in a stack configuration must not detrimentally affect the ultimate clamping of the clip on a plurality of wires.
One prior solution for interconnecting clips in such a manner is disclosed in U.S. Pat. No. 3,722,670 in which a clip assembly utilizes an elongated strand of plastic filament along each lateral edge of the stack. The plastic filament is inserted into pre-formed notches on each side edge of each clip of the stack. However, the plastic filament is held in the notches only by frictional forces. Therefore, any pulling force or tension applied to the stack of clips, such as the forces applied while winding or unwinding the clip stack or indexing the clip stack into a clinching tool, would act to dislodge the filament from the notches of individual clips and thereby misalign or separate those clips from the clip assembly. The plastic filament interconnection as disclosed in U.S. Pat. No. 3,722,670, being merely frictionally engaged within the side notches of each clip, does not sufficiently interconnect the clips for use in an industrial application.
Another prior solution to the above-described problem is disclosed in U.S. Pat. No. 4,508,220 in which the individual U-shaped clips of a clip stack are interconnected by a small diameter flexible metal wire which is welded or otherwise secured to the crown portion of the clips by a metal to metal bond. While such an interconnection may provide the adequate strength and flexibility required of a stack of clips, a problem with the arrangement as disclosed in this patent is that when the leading clip is severed from the remainder of the stack, the severed interconnecting wire welded to the crown portion of each clip presents a sharp, abrasive edge which is a source of injury to workers and which may cut or tear the fabric placed over an innerspring mattress constructed using such a clip.
As evidenced by the above background, there still exists a need for an improved sheet metal clip and a method for interconnecting such clips to form a stack which overcomes these identified shortcomings while still providing a strong and flexible interconnection which does not inhibit the effective clamping of wires as applied with a clinching tool.